1. Field of the Invention
The present invention relates to a zoom lens which is suitable for use in a broadcasting television camera, a video camera, a digital still camera, and a silver-halide film camera, and also to an image pickup apparatus including the zoom lens.
2. Description of the Related Art
Hitherto, for an image pickup apparatus such as a television camera, a silver-halide film camera, a digital camera, and a video camera, there is proposed a zoom lens including, in order from an object side to an image side, a positive first lens unit having a focus unit, a negative second lens unit for zooming, a positive or negative third lens unit for correcting image plane variation due to the zooming, and a positive fourth lens unit for image formation.
In particular, there is proposed a zoom lens in which the first lens unit includes, in order from the object side to the image side, a fixed negative first lens subunit, a positive second lens subunit for focusing, and a fixed positive third lens subunit, which is advantageous for suppressing a variation of performance depending on an object distance, suppressing a variation of an angle of field due to focusing, and achieving a wider angle of field.
Japanese Patent Application Laid-Open No. H09-15501 discloses an embodiment having an angle of field of 78° or smaller at a wide angle end. The first lens subunit includes at least one positive lens, and the second lens subunit includes at least one positive lens and a cemented lens, so as to achieve good optical performance over the entire zoom range and the entire object distance range.
Japanese Patent Application Laid-Open No. 2009-42346 discloses an embodiment having an angle of field of 99° or smaller at the wide angle end. An aspherical lens is appropriately disposed in the second lens subunit, so as to obtain high optical performance over the entire object distance range.
Japanese Patent Application Laid-Open No. 2000-321496 discloses an embodiment having an angle of field of 78° or smaller at the wide angle end. Aspherical lenses are disposed in the first lens subunit and in the third lens subunit, so as to achieve high optical performance over the entire zoom range.
Japanese Patent Application Laid-Open No. 2001-21804 discloses an embodiment having an angle of field of 78° or smaller at the wide angle end. Aspherical lenses are disposed in the second lens subunit and in the third lens subunit, and refractive powers of the first lens subunit to the third lens subunit are appropriately set, so as to achieve high optical performance over the entire focus range.
Japanese Patent Application Laid-Open No. 2001-116993 discloses an embodiment having an angle of field of 74° or smaller at the wide angle end. Lateral magnifications and focal lengths of individual lens units are appropriately set, so as to achieve a reduction of a variation of an angle of field due to focusing.
Japanese Patent Application Laid-Open No. 2012-113139 discloses an embodiment having an angle of field of 75° or smaller at the wide angle end. Refractive powers and glass types of the first lens unit and the second lens unit are appropriately set, so as to achieve a wide angle of field, a high zoom ratio, and high optical performance over the entire zoom range.
Japanese Patent Application Laid-Open No. 2005-249974 discloses an embodiment having an angle of field of 81° or smaller at the wide angle end. Lens configurations of the first lens subunit, the second lens subunit, and the third lens subunit are appropriately set, so as to achieve reductions in size and weight of the first lens unit while maintaining high optical performance.
Japanese Patent Application Laid-Open No. H10-31157 discloses an embodiment having an angle of field of 75° or smaller at the wide angle end. The second lens unit is divided into a second lens unit A and a second lens unit B, and an interval between the lens units is changed in zooming, so as to achieve reductions in size and weight of the entire lens system while maintaining a variation of performance to be small over the entire zoom range and the entire focus range.
Japanese Patent Application Laid-Open No. H06-242378 discloses an embodiment having an angle of field of 64° or smaller at the wide angle end. Focal lengths and glass types of the first lens subunit and the second lens subunit are appropriately set, so as to achieve a lens unit having a high zoom ratio, a wide angle of field, and a short distance at close range.
In Japanese Patent Application Laid-Open No. H09-15501 and Numerical Embodiments 1 and 2 of Japanese Patent Application Laid-Open No. H06-242378, in order to maintain high optical performance over the entire zoom range and the entire focus range even when a wider angle of field and a higher zoom ratio are achieved, the first lens subunit includes at least three lenses in total including one positive lens and two negative lenses.
In addition, in Numerical Embodiment 3 of Japanese Patent Application Laid-Open No. H06-242378, the first lens subunit includes two negative lenses, and the second lens subunit includes one positive lens and one cemented lens. The first lens subunit has a relatively simple structure, but it is difficult to suppress a variation of axial chromatic aberration over the entire focus range.